In a conventional thin-film structural body, a conductive thin-film member which is placed on a substrate with a gap from the substrate is formed as described below. That is, a polysilicon film which is used for forming a thin-film member is formed on a sacrifice film formed on a substrate through a single film deposition step without doping impurities therein. Subsequently, impurities having a desired conductive type are introduced to the polysilicon film from its surface through an ion injection method or the like, so that the polysilicon film is made to be conductive. Then, the polysilicon film is introduced to a diffusion furnace with the substrate, and after a high-temperature annealing process is carried out on the polysilicon film, the sacrifice film is removed to form the thin-film member.
In above said conventional thin-film structural body, the polysilicon film used for forming the thin-film member is formed through the single film deposition step without doping any impurities therein, and the impurities are then introduced therein from the surface so as to make the polysilicon film conductive; therefore, the impurity concentration tends to become uneven in the thickness direction. This tendency becomes more conspicuous in particular as the film thickness of the polysilicon film becomes thicker. When the impurity concentration becomes uneven in this manner, a residual stress, a stress gradient and the like in the thickness direction tend to generate in the thin-film member to be formed, resulting in deformation and the like in the thin-film member. For this reason, in the conventional thin-film structural body, complex annealing treatment processes are carried out so as to reduce the residual stress, the stress gradient and the like.
In this manner, the conventional thin-film structural body is accompanied with a problem that complex annealing treatment processes are required so as to reduce the residual stress, the stress gradient and the like, and another problem is that it is difficult to make the film thickness of the thin-film member thicker.